It could be that this poor woman did her OW, AOW, Nitrox, and Rescue all in a row before ever doing a recreational dive. Then she counted her post-certification dives only when she was asked, so it was a total of 6. She also could have never done a boat dive before she boarded this liveaboard, so didn't have a clue about giant strides. By the time everyone finished talking about her behind her back and the DM yelling at her, she might have been so flustered and upset that she wasn't teachable at that point.
It's really too bad the DM didn't take her aside (before yelling at her) and have a quiet conversation about her dive experience and certifications. Instead, he helped set up a hostile environment where only the tormentors were having a good time. <sigh>